The only large hoop you can use for the 350E is the Giga Hoop. This is equivalent to 2 B hoops in size. Designs for the Giga Hoop are split in half, then you need to combine them in the Customizer,making sure you overlap both sides of the design slightly and the join needs to be pretty spot on, otherwise it will be noticeable. You stitch 1 side first, then rotate the hoop, as Ruth has said, and stitch the second side. This is not suitable for FSL.
I use Customiser 1000 giga hoop with my 300e machine I can use any patterns that fit my B hoop on giga hoop will tell you if design not suitable Alsohave buzz explore programme to convert designs so easy
I think the 350e is very much the same as the 300e. This machine will take the Giga Hoop which does larger designs. The only criteria is you need to make sure the operating instructions in your machine are upto date you can download the updates from Janome and Janome Customiser, it has a section in it for the Giga hoop called Easy Gigahoop, there is also a really good instruction blog on the Janome website. The designs are embroidered in halves by rotating the hoop. There are some free designs included in customiser for the gigahoop, plus if you google gigahoop there are other sites with freebies.
Ruth